Ongoing longitudinal studies of young and adult male workers in a tea plantation in Sri Lanka have shown that the rate of periodontal destruction is excessive and that caries is nonexistent. One purpose of the present study is to use a multidisciplinary approach in trying to explain this dichotomy. The possible influence of the diet on the rate of periodontal breakdown and on the absence of caries will be evaluated by examining the preparation and composition of food, as well as by determining the availability of fluorine and other trace elements. The plaque which is associated with active periodontal destruction but which is not cariogenic, will be subjected to various cultural and fluorescence antibody analyses in order to establish the bacterial composition. Since it cannot be ruled out that both the periodontal breakdown and the absence of caries might be explained by factors within the dental and periodontal tissues themselves, extracted teeth and enamel biopsies, as well as samples of saliva will be brought back to the laboratory and subjected to analyses for chemical compostion and structural organization. Biopsies of gingiva in various stages of pathology will be examined for cellular and chemical characteritics and compared with similar specimens from Caucasians. Since the crucial phase in the development of the periodontal lesion is between 15 and 25 years of age, another purpose is to study the effect of mechanical and chemical measures upon the prevention of periodontal disease in three age groups (15, 20 and 25 years). Besides providing data for evaluating the preventive methods, this portion of the study could have a decisive impact on dental public health in Sri Lanka.